Preheat the oven to 350 degrees F.In a medium saucepan over medium heat, sauté the celery and onion in the margarine for 3 to 5 minutes, until tender. Add 3 cups chicken stock, the chicken, petit pois, and carrots and cook, uncovered, for 5 minutes, stirring occasionally. Combine the cornstarch and remaining chicken stock and add to the saucepan. Increase the heat to high and cook, stirring constantly, for 2 minutes until the sauce thickens and becomes bubbly. Add the spinach leaves and pepper and cook 1 more minute until the spinach is wilted. Divide and pour into 2 ungreased 10-inch pie plates.

Roll out the pastry doughs and place 1 over each pie plate. Trim any overlap around the edges and cut 5 (1-inch) slits in each top to allow steam to escape. Bake for 45 to 55 minutes, or until the crust is lightly browned. Let stand for 5 minutes before serving.